In some wireless communication systems, user equipments (UEs) wirelessly communicate with one or more base stations. A wireless communication from a UE to a base station is referred to as an uplink communication. A wireless communication from a base station to a UE is referred to as a downlink communication. Resources are required to perform uplink and downlink communications. For example, a base station may wirelessly transmit data to a UE in a downlink communication at a particular frequency for a particular duration of time. The frequency and time duration are examples of resources.
In a traditional wireless communication system, all messages between two UEs pass through at least one base station, even if the two UEs communicating with each other are in close physical proximity. Device-to-device (D2D) communication has more recently been introduced to allow for UEs in close proximity to directly communicate with each other without using a base station. A group of UEs may form a D2D group and then communicate with one another using D2D communication.
As the number of UEs in a wireless communication system increases, there may be more potential opportunities for using D2D communication.